Automatic telephone system directed with the aid of revertive audio-frequency signals



ZAZMGQ y 27, 194? R. TAYLOR ETAL AUTOMATIC TELEPHONE SYSTEM DIRECTED WITH THE AID 0F REVERTIVE AUDIO FREQUENCY SIGNALS I Filed May 27, 1944 TO BANKS OF THER $ELECTOR5 ITL CTL

IPL

165 'ms. ON 12 165 m 5 OFF '3 INVENTORS \REGINALD TAYLOR seonss THOMAS BAKER BY Z ATTORNEY Patented May 27, 1947 UNITED STATES FREE AUTOMATIC TELEPHONE SYSTEM Di- RECTED WITH THEAID 0F REVER- TIVE AUDIO-FREQUENCY SIGNALS Reginald Taylor and George Thomas Baker,

Liverpool, England, assignors to Automatic 1 Electric Laboratories Inc., Chicago',- lll-. ,-a'corporation of Delaware Application May 27, 1944, Serial Nokt'f 'lg iil In Great Britain -.-liily'8,- 1943 13 Claims. 1

The present invention relates to electrical signalling systems, and offers considerable advantages in its application to automatic telephone systems. Theflinven'tion is moreover particularly suitable for use in small private automatic telewith an automatic switch to cause it during its operation to transmit back to the calling party an audible signal for indicating the identity of the line with which it is associ'ated at any time.

According to another feature of the invention, in an automatic telephone or like Signalling system having connections set up over automatic switches located at a--central point, signalling .arrangements are provided for notifying a calling party of the progress of the movement of an automatic switch and for effecting its arrest when it has reached the appropriate point.

A furtherfeatu re of the invention is that in an automatic telephone or like signalling system having connections set up over "automatic switches located at a central point, a calling party is enabled by suitable separate operations at the substation to prepare a switch for operation, to initiate its movement and to bring'it to rest when it has reached the appropriate point.

Another feature of the invention is that in an automatic telephone or like signalling system having connections set up over automatic switches located at a central 'point the setting of an automatic switch is adapted to be initiated by a signal from a calling substation and-thereupon continues until terminated by a inr-ther signal from the substation or the switch reaches the end of its traveL-the position of the switch being continuously indicated to the calling party.

A still further feature of the invention is that in an automatic telephone or like signalling system'having connections set up over automatic switches located at a central point each station having associated with it a switch having access to all the other stations, each switch is adapted to be operated by locally generated impulses as long as a calling party at the associated station maintains-his line in a characteristic condition 2 'or until the switch reaches the end of its travel, characteristic signals being transmittedbackto the calling-party to-notify him of the progress of the switch.

The invention will be better understood from 'thefollowing.description'oi one method of carrying. it into effect, rei-eren-cebeing had tothe accompanyingdrawi-ng comprising Figs. 1 and 2' in which the invention is-shown applied to a tenline private automatic-exchange ('P. A. X). :Fig. .1 showsthe circuit 05 the local and exchange apparatus provided per subscriber, the circuit of Fig. 1 relating particularly to subscriber No. 5 out of the ten subscribers 'l-Hl on the board, while Fig. '2 shows the circuit of the common services for the board.

Referring now-to-Fig. 1, the P. A. X to be described employs sound-powered hand-microtelephonesea-ch'of whichinclu'des a handset: push button which-is permanently bridged by a condenser. The -restof 'the'instrument merely consists :of a hook or rest on which the handset is accommodated-when not inuse. The dials, bells and induction coils usuallyprovi'ded on P. A. X telephone instruments are dispensed with.

On the P. A. X b'oard,,there is associ'ated 'with "eachline' two-relays C and H, of so-called minor type, and a 12'-1poi-nt-rotary selector switch SS ofthe forward drive type. The only other equipment requiredisthe common services equipment for the board which is shown in Fig. -2 and which consists of an interrupter driven from. a small mains-operatedsynchronous-motor, a tone source comprising an oscillating neon tube; and a rec- 'ti-fier unit (notshownlwhich provides D. G, supply for the line relays and rotary switches.

To-Set' up'a-call the push button on the handset is depressed and is then released. In response tothese operations the rotary switch in theassociated line circuit is caused to step at a speed of the'order of two or three steps persec'ond over the ten lines of the board in turn.= For each step of theswitcn-a tone pulse is applied to the calling line so as to enable the subscriber to count the stepsof the switch and so be aware when ithas positioned itself on the :reauiredv line. When this is reached. the push "button on the handset is again depressed and this results inthe arrest of the switch and-the setting upoi a calling'condition on the desired line. Preferably the wanted artys attention is attracted by continuous tone current irom the exchange equip- .mentextendedover his-line to actuate the serieseonnected.sound-.-poweredtransmitter-and. receiver. The terminationof the tone pulses indicates 3 to the calling subscriber that the called subscriber is being rung.

When the called subscriber answers by taking up his handset and depressing the push button, the calling signal is immediately terminated and conversation may proceed, the push buttons on both the calling and called instruments being held depressed during conversation.

In case the wanted subscriber is busy, the tone pulses continue after the depression of the push button by the calling party. In response therefore to this busy indication the calling party will restore the button and the switch will proceed to step on to its home position when the line circuit will be ready for further calls.

From the above brief description it will be appreciated that the setting up of a call is a completely one-handed operation and requires no manipulation beyond that concerned with the push button.

Considering now the circuit operation and referring first to the common services circuit of Fig. 2, the mains-driven synchronous motor SM drives the two interrupters II and I2, the former providing 165 m. s. earth pulses at spacings of the same order for the purpose of stepping the line circuit rotary switches and the latter providing on lead ITL 165 m. s. tone pulses which are synchronised with the stepping impulses applied to lead IPL. For ringing purposes continuous tone is used, and this is available from lead CTL.

Referring now to Fig. 1, when the handset push button of subscriber No. 5 is depressed, push button contacts PBI loop the line and operate the line relay C. A circuit is then completed over bank and wiper SS5 of the rotary switch SS to advance the switch wipers to position 1 in which relay H is operated by way of its two windings in series via wiper and bank SS4 and thereupon looks over its lower winding.

When the push button is released, relay C falls away and if at this time there is an earth on the pulse lead IPL, relay H will remain held and will only release to connect up this lead to the bank SS5 when the earth is removed from lead IPL, relay H thus providing a pulse guard feature.

The next earth pulse received over lead IPL moves the SS switch to position 2 from which position access can be had over wipers and banks SS2 and SS3 to the line of subscriber No. I. When the switch reaches position 2, a tone pulse is transmitted over lead ITL and bank and wiper SSI to the calling partys receiver, and since as previously mentioned these tone pulses are synchronized with the stepping pulses, the tone pulse will persist until termination of the stepping pulse which advanced the switch to position 2.

For each step of the switch over the lines of the board a tone pulse is returned to the calling party and, assuming that subscriber No. 8 is required, after eight tone pulses have been heard, 1. e. when the SS switch has been set to position 9 which connects with subscriber 8, the push button is again depressed and this re-operates relay C which opens the switch driving circuit. At the same time a testing circuit is provided for relay H over wiper and bank SS4 to the wanted line and if this line is free, relay H will energise in series with the H relay of the wanted line, the circuit extending over wiper SS4 in position 9, and the multiple wiring to the bank SS4 in No. 8 line circuit. In this circuit the P lead No. 8 is wired back to the home position of wiper SS4 in the same manner that P lead No. is wired back as shown to the home position 0 of 4 wiper SS4 in No. 5 line circuit. Hence, in No. 3 line circuit the circuit will extend via bank and wiper SS in home position, upper winding of relay H and bank and wiper SS5 to battery via the switch magnet SSlvI.

The calling relay H in operating switches the calling line through to the wipers and banks SS2 and SS3, disconnects the tone pulse circuit to the calling party and further disconnects the magnet driving circuit, while relay H of the called line No. 8 in operating extends continuous tone over lead CTL onto line No. 8.

When the called subscriber answers by depressing his push button, the associated C relay operates and steps the relevant SS switch to the second position, thus cutting off the calling signal at wipers and banks SS2 and SS3 and at the same time completing a conversational path. In addition the called partys relay H is held independently of the SS switch banks and wipers.

During conversation the C and H relays of both subscribers are held operated, and at its conclusion the restoration of the push buttons releases the C relays whereupon the H relays after performing their pulse guarding feature, if required, release in turn and complete homing circuits for the SS switches from the common lead IPL.

In case the wanted line is busy, on the operation of the relay C in the calling line circuit after the requisite number of tone pulses have been heard, relay H is unable to operate since, owing to the fact that the SS switch in the called line is off-normal, the battery potential normally supplied to the relevant P lead is disconnected. With the calling line circuit relay H normal the tone pulses continue to be sent to the calling subscriber over bank and wiper SSI. The motion of the switch SS is, however, halted due to the operation of relay 0.

When subsequently the calling party restores his push button, relay C releases, whereupon relay I-I releases in turn, after fulfilling its pulse guard function, and re-connects the pulse lead IPL to bank SS5 and the switch SS proceeds to rotate through to the home position.

Special facilities offered by the telephone system embodying the invention will now be considered.

Considering first the so-called step-on facility, if for example subscriber No. 5 after gaining access to subscriber No. 8 wishes to speak to subscriber No. 9 or Hi, all that is necessary after terminating the conversation with subscriber No. 8 is for him to continue to hold his handset against his ear and also to release his push button, whereupon the SS switch will step on and will return a tone pulse for each step. After the one or two steps necessary to gain access to subscriber No. 9 or 10 have been taken, the push button is again depressed and the called subscriber is then rung in the usual manner.

In case the subscriber wishes to change over to asubscriber having a lower number, say from subscriber No. 8 to subscriber No. 3, it will be simpler for him to release the set-up in usual manner by releasing the push button, and then a few seconds later to re-initiate a call to the subscriber No. 3.

A priority facility may be readily obtained by permanently strapping the H3 contacts on the line circuits of all subscribers entitled to this facility, in which case cut-in to the desired line will take place regardless of whether it is busy or not. 1

In order to provide a conference facility, a

certain bank position, say thatcorresponding to line ID, will be allocated for conference-purposes, and its P lead will be permanetly connected to a low resistance battery. The various subscribers required for conference will be called up in turn and will be told to effect connection with line It. When they do so, all their H relays will operate from the resistance battery and conference ma then take place. This arrangement will, of course, reduce the capacity of the board to nine lines.

As an alternative to the tone pulses, arrangements might be made for audible announcement to-calling parties'of the numbers of the lines as they are successively connected with, but this would involve appreciable additional expense and complication.

Withregard to the telephone instruments, with the circuit as shown, if a subscriber places his handset to his ear and fails to depress the push button, there is always the possibility of his being called, and he would then at least receive an uncomfortably loud sound in hisear. This possible trouble could be readily overcome by providinga non-linear resistance shunt such as a-smalldry plate rectifier across the handset receiver and by arranging-for the tone pulsesto be of smaller amplitude than the continuous ring-- ing tone current, so that. for tone pulses the non-linear resistance shunt would have a very small shunting effect, but for continuous ringing current the shunting effect would be much greater. Under these circumstances the transmitter would serve as the main calling device on each handset.

If the necessity for holding the push button depressed during conversation is irksome to sub scribers, the difficulty may be readily overcome b providing locking facilities on the push button.

The advantages of this arrangement are however probably outweighed by its disadvantage, since special action is necessary to restore the push button to normal after each call. This final operation is likely to be forgotten in many instances thus leaving the line concerned in a permanently busy condition and also holding the line to which connection has previously been made.

A more satisfactory alternative therefore is to makeuse of a cradle'switch of ordinary type for closing the line circuit, only the control of the movement of the switch being elfected from the push button which in this case is arranged to open normally closed contacts in the line circuit. The likelihood of the-line equipment being tied up by a forgetful subscriber is then no greater than with a normal instrument.

In regard to the line circuits, these are of a novel kind in that the normal switch operating circuit is the same as the homing circuit and while movement to a desired line is taking place there are no relays operated in the line circuit concerned.

It will be appreciated that a board according to the invention, could, with some modification, be adapted to give tie line facilities to another board or boards of the same type.

From the foregoing description" it will be seen that a particularly inexpensive and at the same time efficient P. A. X board has been provided in which the total of the local and exchange apparatus per lineis in effect ahandset, twov minor type relays and a small rotary selector switch, andin-which, due'to-the elimination of link circuits which form an economic point of view are gea -mes normally limited to one or two perte'n lines, all the subscribers on-the board can be on conversation pairs at the same time, that is to say, full availability-conditions are obtainable at all times.

The invention-is not limited in application to the-use of sound-powered telephones as ordinary telephone instruments might be used. For P. A. X use this would, however, increase :thecost both-of the board and ofthe subscribersinstruments, since standard ringing andring trip arrangements would be needed in the line circuits, induction coils and bells would 'berequiredin the telephone instruments.

The invention is moreover not limited to cases where only a single digit is required as the general principles could readily be applied to larger networks where two or even more digits are-involved in turn and control is effected by repeated operation of the push button. Furthermore the invention is not restricted to private exchange networks and may infact offer valuable. advantages in connection with rural networks where the standard of maintenance of the sub-- scribers lines is not sufiiciently high to permit satisfactory calling in the normal manner by trains of impulses but is good enough to permit tone signals'to be effective and enable control to becarried out by a single opening and closing of the line circuit.

What we claimas newand-desire to secure by Letters-Patent is:

1. In a telephone system, a plurality of telephone substations each including a receiver, an exchange, lines connecting each'of the substations to 'the'exchange, switching means in the exchange having a plurality of selecting positions each corresponding to one of said substations, means controlled over acalling one of said lines for initiating the operation ofsaid switching means, means in theexchange for thereafter causing said switching means to be successively advanced through said plurality of selecting positions and for concurrently transmitting series of audio frequency impulses over the calling line, each of said impulses corresponding to one of said selecting positions, said impulses causing audible signals to be produced by the receiver at the calling substation to indicate the progress of said switching means, saidsecond means being controlled over the calling line to stop the advancement of said switching means when it hasreached a positioncorresponding to a desired station.

2. In a telephone system as claimedin claim 1, a testing circuit associated with said switching means, and means controlled over said testing circuit for causing the transmission of said audio frequency impulses to be continued in the event that said switching'means is stopped in a position corresponding to a station that is busy.

3. In a signaling system, a control station, a controlled station including switching means having a plurality of selecting positions, a line extending between said stations, means at said control station for completing a direct current circuit over said'line to cause said switchingmeans to perform an initial switching operation, said switching means being thereafter responsive to subsequent opening of said direct current circuit at the control station to advance itself through said pluralityof selecting positions and to transmit a series of alternating'current impulsesover said line, means at said control'station responsive to said impulses for indicating the progress of saidswitching means, the advancement of said switching means being stopped in response to the 7 reclosure of said direct current circuit at the control station when a desired selecting position has been reached.

4. A signaling system as claimed in claim 3 in which said switching means is arranged to return to its initial position in the event that said direct current circuit is not reclosed at the control station.

5. A signaling system as claimed in claim 3 in which said switching means is responsive to a second opening of said direct current circuit to advance itself through subsequent selecting positions.

6. In a telephone system, a plurality of telephone stations, a selector switch for each of said stations, each of said switches having a normal, an answer, and a plurality of calling positions,

, means controlled by a calling one of said stations for advancing its corresponding selector switch into any one of said calling positions to associate said calling station with a called station, means operated in response to said association for signaling the called station, and mean responsive to an answer by the called station for advancing its corresponding selector switch into the answer position to stop the signaling thereof and to complete a talking circuit between said two stations.

7. In a telephone system, a plurality of tele-- phone stations each including a receiver, a selector switch associated with each of said stations, each of said switches having a plurality of selecting positions each corresponding to one of said stations, means controlled by a calling one of said stations for initiating the operation of its associated selector switch, common mean thereafter causing said selector switch to be successively advanced through said plurality of selecting posi-- tions and transmitting a series of audio frequency impulses to the calling station, said impulses causing audible signals to be produced by the receiver at the calling station whereby a subscriber thereat can determine the progress of said selector switch, said first means being controlled by the calling station to stop the advancement of said selector switch when it has reached a selecting position corresponding to a desired station.

8. A telephone system as claimed in claim '7 in which said first means comprises a relay which is operated and restored to initiate the operation of said selector switch, said relay being reoperated to stop the advancement of said selector switch by said common means,

9. In a telephone system, a plurality of telephone stations, a pair of relays and a selector switch for each of said stations, each of said switches having a normal, an answer, and a plurality of calling positions, a first relay of each of said pairs being operative under the control of its corresponding station to cause the corresponding selector switch to be advanced into any of said calling positions in order to associate two of said stations, the second relay of the pair corresponding to the calling one of said two stations operating to prepare a talking circuit between said two stations and the second relay of the pair corresponding to the called one of said two stations operating to signal the called station in response to said association, the first relay of the pair corresponding to the called station operating in response to an answer therefrom to cause the corresponding selector switch to be advanced to the answer position in order to stop the signaling of the called station and to complete the talking circuit between said two stations.

10. A telephone system as claimed in claim 9 including circuit arrangements preventing operation of the second relay of the pair corresponding to the calling station if the called station is in use, thereby causing a busy indication to be returned to the calling station and preventing interference with the called station.

11. A telephone system as claimed in claim. 9 including circuit arrangements normally preventing operation of the second relay of the pair corresponding to a calling station if the calling position to which the selector switch thereof is advanced is occupied by a selector switch corresponding to another station, and further circuit arrangements causing the second relays of the pairs corresponding to calling stations to operate when the selector switches thereof are advanced to particular calling positions despite the busy condition thereof, whereby conference service may be established between three or more of said stations.

12. In combination, a first station, a second station including a progressively movable device having a plurality of operating positions, a line extending between said stations, means at said first station for completing a direct current circuit over said line, means at said second station operated in response to a subsequent opening of the direct current circuit completed over said line from said first station for causing said device to be moved through said plurality of operating positions and for causing a series of impulses each comprising alternating current to be transmitted over said line, means at said first station responsive to said impulses for indicating the progress of the movement of said device, the movement thereof being stopped by the operation of said second means in response to the reclosure of the direct current circuit at said first station when a desired operating position has been reached.

13. In combination, a first station, a second station including a progressively movable device having a plurality of operating ositions, a line extending between said stations, means at said first station for completing a direct current circuit over said line, means at said second station operated in response to a subsequent opening of the direct current circuit completed over said line from said first station for causing said device to be moved through said plurality of operating positions and for causing a series of audio frequency impulses to be transmitted over said line, means at said first station responsive to said im pulses for audibly indicating the progress of the movement of said device, the movement thereof being stopped by the operation of said second means in response to the reclosure of the direct current circuit at said first station when a desired operating position has been reached.

REGINALD TAYLOR. GEORGE THOMAS BAKER.

EFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

